Background: Natural disasters have profound effects on health and require medical intervention as part of relief operations. The world's populations are becoming increasingly vulnerable to extreme weather events, which are responsible for most natural disasters. The El Niño Southern Oscillation (ENSO) is the most prominent global climate system associated with year-to-year weather variability and extreme events. We have estimated the burden on human health of natural disasters associated with ENSO.
Methods: We used time-series regression analysis of the relation between El Niño years and the annual rates of persons affected by natural disasters per 1000 population during 1964-93, globally and also by region and disaster type. Correlations between sea-surface temperature (SST) anomalies (index of ENSO) and the rates of persons affected by natural disasters per 1000 population were determined globally, by region and by disaster type.
Findings: The rate of persons affected by natural disasters worldwide is strongly associated with ENSO; rates are greater during the first El Niño year (p = 0.05) and the following year (p = 0.01) than in the pre-Niño year. The correlation between rates of persons affected by natural disasters and SST anomalies in the Eastern Pacific (a key ENSO indicator) is highest in the last quarter of the previous year (r = 0.53, p < 0.01). These associations are strongest in South Asia, the region where more than 50% of all disaster victims live. Worldwide, rates of persons affected by drought/famine (half of all disaster victims) and by volcanic eruptions show significant associations with the ENSO cycle, being highest in the post-Niño year and El Niño year, respectively, and being significantly associated with SST anomalies.
Interpretation: The strong relation between ENSO and populations affected by natural disasters can be described as a "natural disaster cycle". Determining the phase in this cycle, using SST from the Eastern Equatorial Pacific, could benefit disaster preparedness on a global scale, for South Asia in particular, and for all populations affected by drought/famine and volcanic disasters.